1. Field of the Invention
The present invention is related to a sunlight sensor which detects an amount of sunlight, and more specifically, to a sunlight sensor used in the control of an air conditioner installed in a vehicle, and which distinguishes the condition of the sunlight, including the angle of elevation of the sunlight.
2. Description of the Related Art
In an air conditioner installed in a vehicle, the temperature inside the vehicle is measured, and automatic controls optimize the temperature inside the car. In addition to the interior temperature, information related to the sunlight entering the vehicle is also an important part of the thermal environment inside the vehicle. When there is much sunlight entering through a window, it is necessary for the cooling device to work harder. That is, the output of an air conditioner is controlled based on the direction of incidence of the sunlight. It is desirable, when using a sunlight sensor in this manner, to reduce the air conditioner output when the sunlight is incident from directly above and to make the output peak when the elevation angle of the sun is in the region of 45.degree..
To optimize air conditioning with a vehicular air conditioner, it is desirable to not only detect the amount of sunlight with the sensor, but also to control the air conditioner output according to the direction of the sunlight. Specifically, it is desirable to reduce the output when the sunlight is incident from directly above and to make the output peak when the elevation angle is in the region of 45.degree..
In a prior art sunlight sensor, as disclosed in Japanese Unexamined Patent Publication No. 2-99835, a light-receiving element 39, such as a photodiode, which outputs an electrical signal responsive to the amount of sunlight is mounted at the bottom part of covered-dish-shaped eyelet 38 to which lead wire 37 is connected. Light-receiving element 39 has a light-receiving surface 40 on its top surface connected, via a bonding wire 41, to a lead wire 42. Lead wire 42 is held by the borosilicate glass that fills the bottom part of the covered-dish-shaped eyelet 38. On the outer circumference of the covered-dish-shaped eyelet 38 is welded a cylindrically shaped eyelet 45 which is fitted at its opened top end around a lens 44 which covers the light-receiving surface 40 of the light-receiving element 39. By imparting a special shape to this lens 44, the amount of sunlight (not shown in the drawing) which reaches the light-receiving surface 40 via lens 44 increases as the angle of incidence of the sunlight with respect to the perpendicular increases, with the output becoming maximum when the sunlight is at a prescribed inclination.
In a sunlight sensor as described above, by means of the shape of the lens which covers the light-receiving surface of the light-receiving element, the output is maximum when the sunlight is incident at a certain prescribed angle.
However, with this configuration, to obtain the desired elevation angle characteristics, it is necessary to provide a highly precise lens shape, which is extremely costly.
Furthermore, because the output, which is based on the amount of sunlight incident to the total light-receiving surface, is greatly influenced by the relative position relationship of the lens and the light-receiving surface, positioning of the lens becomes difficult. For that reason, extra light other than the desired light strikes the light-receiving surface, thereby preventing the sufficient achievement of the desired elevation angle characteristics.
In recent years, with advances being made in semiconductor technology, there has been a strong demand for the application of this technology to the achievement of the desired elevation angle characteristics in the detection of sunlight.
In the above-described prior art, the output, which corresponds to the amount of sunlight incident on the total light-receiving surface, is greatly influenced by the relative position relationship of the lens and the light-receiving surface, so that the positioning of the lens becomes difficult. Furthermore, stray light, other than the desired incident light, strikes the light-receiving surface, thereby making the sufficient achievement of the desired elevation angle characteristics difficult.
To obviate the above problems, a practical sunlight sensor using semiconductor technology is desirable.